1. Field of the Invention
The present invention relates to a data processing apparatus and method, and a data transmitting/receiving apparatus. More specifically, the present invention relates to a data processing apparatus and method for receiving an electromagnetic wave which is Amplitude Shift Keying (ASK)-modulated corresponding to a predetermined data, rectifying such electromagnetic wave as a power source, and transmitting such data by controlling a load condition to the power source, and a data transmitting/receiving apparatus and method for transmitting the ASK-modulated electromagnetic wave corresponding to the predetermined data with the predetermined transmitting means and receiving the data by detecting any change of the load condition of the transmitting means.
2. Related Background Art
Introduction of a reader/writer (R/W) and an IC card for data exchange on non-contact basis is now under discussion for a ticket inspecting machine, security system and electronic money system.
In the reader/writer (R/W), the carrier is modulated with the data to be transmitted by the predetermined system and the modulated electromagnetic wave (for example, magnetic field) is radiated to an IC card.
The IC card receives such electromagnetic wave and demodulates the received electromagnetic wave to the original data by the corresponding demodulating system and processes such data within the predetermined electronic circuits. Upon completion of processing of such data, the IC card transmits a response to such data to the R/W, causing to receive such data.
A certain kind of IC card explained above is a so-called batteryless type IC card which is not provided with batteries and utilizes the power of the electromagnetic wave obtained by rectifying the wave received as a DC power source.
In the case of transmitting the data to the batteryless type IC card, R/W utilizes the Phase Shift Keying (PSK) and Frequency Shift Keying (FSK) modulation method in which the modulated wave can easily be converted to the stable DC signal or amplitude of the modulated wave is constant. As explained above, by keeping the amplitude of the modulated wave constant, voltage fluctuation of the power source obtained by rectifying the electromagnetic wave received by the IC card can be reduced and thereby the stable power can be supplied to the electronic circuits.
However, the use of the PSK or FSK modulation system will result in the possibility that the frequency spectrum of the electromagnetic wave are transmitted or received spread over a wide frequency band to potentially give adverse effects on the existing communication system and the other electronic devices.
Moreover, it is also possible to restrict the frequency band occupied by the electromagnetic wave to a predetermined range, but such restriction will result in difficulty considered as a problem in transmission and reception in the higher communication rate. For instance, if the non-contact card system explained above is introduced into the ticket inspecting apparatus, too much time is required to process the data.
Alternatively, it has also been proposed for the R/W to radiate two electromagnetic waves indifferent frequencies, one electromagnetic wave for supplying power and the other wave for data communication. However, this approach requires that the occupied frequency band become wide due to the use of two different frequency bands. Moreover, the electronic circuits will likely become large because the two kinds of electromagnetic waves in different frequencies are transmitted or received.
The present invention has been proposed in view of the background discussed above to realize information communication with a higher communication rate and supplying satisfactory power source to an IC card while keeping the narrow occupied frequency bandwidth by utilizing the ASK modulation method wherein the degree of modulation is kept to less than 1.